Some crops, particularly legumes such as soybeans, are desirably cut close to the ground, because some of the bean bearing pods are located there, and it is desirable to harvest as much of the crop as is practical. Other crops, particularly grasses such as wheat, oats, and barley, are desirably cut higher above the ground, for instance, at a height typically several inches above the ground, because the grain bearing heads are at the top of the plant. And, if the straw is not to be baled, it is typically desirable to cut at a higher height, to limit the amount of straw which is cut and inducted into the harvesting machine. For instance, if straw is not to be baled, it may be desirable to use a cutting height greater than about 7 inches above the ground, or, as another example, within a range of about 10 to 15 inches above the ground. Typically, when cutting crops such as soybeans close to the ground, the cutter bar is supported in a flex or floating mode wherein it is allowed to freely move vertically relative to the header within a limited range of travel. In contrast, at the higher cutting heights, the cutter bar is typically fixed to the header so as to be unable to flex or float.
To increase productivity, the trend has been toward the use of wider or longer headers such that more crops are harvested during each pass of a harvesting machine over a field. However, with the lengthening of the headers, for instance, to lengths of up to 40 feet, the risk of the header contacting the ground is increased, due to a variety of factors, particularly, unevenness of the ground. Currently, it is well known for a header to include an automatic header height control system which is used when the header is lowered to a lower cutting height for beans and the like, and the cutter bar in a flex or float mode. Generally, in operation, such control will use information relating to sensed contact with the ground to determine differences in level or slope of the ground, and irregularities of the ground surface, and automatically raise and lower the header for maintaining the cutter bar in desired relation to the ground, and for maintaining a desired down pressure on the cutter bar. Such systems typically utilize a side-by-side array of skid shoes or plates in connection with the floating cutter bar, which skid shoes extend just below the cutter bar for sensing or contacting the ground, and when one or more of the skid shoes contact the ground sufficiently to move the cutter bar upwardly, the cutter bar will at the same time provide inputs to the header height control system through a sensor, to enable the system to determine whether to raise or lower the header.
When the header is at a height for cutting grasses such as wheat, the cutter bar is located higher above the ground, and thus the array of skid shoes is also located above, and thus not in contact with, the ground, such that the automatic height control system is rendered ineffective. At such higher cutting heights, the cutter bar is typically fixed in a raised position so as not to flex or float, and to facilitate crop flow onto a lower pan of the header. As a result of the raised position of the cutter bar, if the automatic header height control is operational, false ground contact information may be provided to the control. As a result, the header height control is typically turned off or operated in a manner which disregards inputs resulting from the fixed cutter bar. However, even at such heights, as a result of the great widths or lengths of the headers and elevational variances in fields, it has been found that there still exists the possibility or danger of the header contacting the ground, particularly of the ends of the header contacting the ground. As a result, it would be desirable for the automatic header height control, and other controls which use such ground proximity information, to be operable with the header at such heights, for automatically adjusting the header height or other parameters for avoiding such contact. It would also be desirable to have a ground sensing capability which works at a greater distance below the cutter bar, for instance, about 5 or more inches therebelow.
Accordingly, what is sought is apparatus for enabling operation of an automatic header height control with a cutter bar fixed in position, such as when the header is positioned at a higher elevation such as for cutting grasses such as wheat, which provides one or more of the desired properties, and overcomes one or more of the problems, set forth above.